Crystal production



Oct. 28, 1958 c. c. LARSON CRYSTAL PRODUCTION Filed Oct. 15. 1954 IN VEN TOR. CHRIS T/A N C. L A RSON BY United States Patent CRYSTALPRODUCTION Christian Charles Larson,

Fort Wayne, Ind., assignor to International Telephone The presentinvention relates to crystal production, and more particularly to amethod for manufacturing crystals which may be used as elements oftransistors.

Conventional techniques for fabricating crystals from such materials asgermanium, silicon and the like is to melt the basic material in acrucible and then touch the molten material with a seed crystal and drawthe latter upwardly and away from the molten material at a sufiicientrate to continuously draw or grow a crystal. Such methods have been usedsuccessfully in the past, but are attended with considerabledifiiculties in the cases where in silicon materials are used to producethe crystals.

Melted silicon in particular is of such high temperature that the usualcrucibles are damaged or destroyed. No known crucible materials have yetbeen developed which will reliably withstand the high temperatures ofmolten silicon.

An object of the present invention is to provide a method for producingcrystals without the need of a crucible.

It is another object of this invention to produce crystals from moltenmaterial in such a manner that the solid raw material constitutes thecrucible for the molten material.

It is still a further object of this invention to utilize electronbombardment for melting a predetermined portion of a block of rawcrystal material from which a finished crystal may be drawn.

Other objects will become apparent as the description proceeds.

To the accomplishment of the above and related objects, the inventionmay be embodied in the forms illustrated in the accompanying drawings,attention being called to the fact, however, that the drawings areillustrative only, and that specific change may be made in the specificconstructions illustrated and described, so long as the scope of theappended claims is not violated.

In the drawings:

Fig. 1 is a vertical sectional elevation of an embodiment of thisinvention;

Fig. 2 is a top plan View thereof;

Fig. 3 is a diagrammatic illustration of an electron gun used in theapparatus of Fig. 1; and

Fig. 4 is a perspective illustration showing one step of the method ofdrawing a crystal.

Referring to the drawings, the apparatus comprises an evacuated bell jar1 which is hermetically sealed to a metallic base 2. A shaft or rod 3 isreciprocably mounted in the top portion of the bell jar by means of asuitable threaded connection with a hermetically sealed coupling 4.Suitable constructions for reciprocating the rod 3 from a positionoutside of the bell jar 1 are wellknown to the art and in particular aredescribed in a publication entitled Vacuum Equipment and Techniques byGuthrie and Wakerling, published by the McGraw-Hill Book Company andcopyrighted in 1949.

A plurality of suitable electron guns 5 are circumferentially mounted onthe top portion of the bell jar in 2,858,199 Patented Oct. 28, 1958 sucha manner as to direct high density electron beams along the pathsindicated by the dashed lines 6. These electron guns 5 may be ofconventional construction and correspond to the electron gun arrangementdisclosed in Gardner Patent 2,128,581. A suitable gun construction isdiagrammatically illustrated in Fig. 3 wherein electrons emitted by acathode 7 are concentrated into a pencil-like beam by an anode 8 andaccelerated by both this anode 8 and another anode 9. As will becomeapparent from the following description, this pencil-like beam must beof high density.

On the base 2 of the bell jar 1 is placed a block 10 of silicon,germanium, or the like material in such position that the centralportion thereof will be bombarded by the respective electron beams 6.These beams 6 are of such high density as to melt the central portion ofthe block 10. The beams are so controlled that only the central portionof the block is melted, whereby the block serves as a crucible for themelted portion.

A seed crystal of the type which is to be finally produced is clamped bysome suitable means in the lower end of the reciprocable rod 3, and sucha starter or seed crystal is indicated in Figs. 1 and 4 by the referencenumeral 11. The rod 3 is lowered until the seed crystal 11 just touchesthe molten material, and is then withdrawn upwardly at a slow rate whichwill allow the molten material to continuously form on the lower end ofthe seed crystal. Continued withdrawal of the seed crystal therebyostensibly draws or pulls a suitable crystal structure from the solidblock. During this pulling operation, the beams 6 are trained onto theareas surrounding the drawn crystal, whereupon the operation may becontinued until the block 10 is substantially consumed.

Since the block 10 acquires an electrostatic charge from the electronbeams 6, it is desirable to provide a conductive return path for currentfiowfrom the base 10 to one of the gun anodes, such as the anode 9. Awire 12 is shown as providing this conductive path. While there has beenshown a plurality of individual electron guns 5, it is possible toutilize a single electron gun of annular configuration which willproduce a tapered, hollow electron beam for melting the block 10 in thevicinity surrounding the seed crystal 11.

By performing the operation in a vacuum, impurities are prevented fromentering the finished crystal. By withdrawing the crystal from thecentral portion of a solid block, the latter also serves as thecrucible, thereby avoiding the prior art problem of preventingdestruction of crucibles when materials, such as silicon, are melted.

What is claimed is:

1. The method of fabricating crystals comprising born barding a portionof a block of material from which a crystal is to be made withelectrons, said bombardment serving to melt said portion, said portionbeing disposed in one block surface inside the perimeter thereof, anddrawing a seed crystal from said melted portion, the unmelted portion ofsaid block serving as a crucible for the melted portion.

2. The method of fabricating crystals comprising selective melting acentral portion of a block of material from which a crystal is to bemade, said portion being disposed in one surface between the lateralblock sides, drawing a seed crystal from said melted portion, theunmelted portion of said block serving as a crucible for the meltedportion, and continuing to melt said block in the perimetral vicinity ofthe crystal being drawn.

3. The method of fabricating crystals from a block of material fromwhich a crystal is to be made, said method comprising positioning aself-supporting block of said material in an evacuated containerfocusing an electron beam on the upper surface of said block, increasingthe energy in said beam until a pool of said material meltsv in saidupper surface within the perimeter of said upper surface of the blockwhereby said block serve as a crucible for the pool of melted material,partly immersing in said pool a seed crystal of said material, andlifting the seed crystal from thepool at the rate of solidificationofthe material uplifted from the pool.

References Cited inthe file of this patent NITED STATES PATENTSKjellgren May 3, 1949 4 Malone June 7, 1949 Sparks et al. Mar. 17. 1953Imber July 28, 1953 Sobek Apr. 6, 1954 Little et al. July 13, 1954FOREIGN PATENTS France Mar. 10, 1954 OTHER REFERENCES Bell Tel, Lab.Inc. and Western Electric Co. Inc., Transistor Technology, part II,chapter 7, July 1952.

1. THE METHOD OF FABRICATING CRYSTALS COMPRISING BOMBARDING A PORTION OFA BLOCK OF MATERIAL FROM WHICH A CYRSTAL IS TO BE MADE WITH ELECTRONS,AND BOMBARDMENT SERVING TO MELT SAID PORTION, SAID PORTION BEINGDISPOSED IN ONE BLOCK SURFACE INSIDE THE PERIMETER THEREOF, AND DRAWINGA SEED CRYSTAL FROM SAID MELTED PORTION, THE UNMELTED PORTION OF SAIDBLOCK SERVING AS CRUCIBLE FOR THE MELTED PORTION.